Tissue-specific developmental regulation of protein kinase C isoforms

Generation and Characterization of a Novel Prkcd-Cre Rat Model

Activity of central amygdala (CeA) PKCδ expressing neurons has been linked to appetite regulation, anxiety-like behaviors, pain sensitivity, and addiction-related behaviors. Studies of the role that CeA PKCδ+ neurons play in these behaviors have largely been carried out in mice, and genetic tools that would allow selective manipulation of PKCδ+ cells in rats have been lacking. Here, we used a CRISPR/Cas9 strategy to generate a transgenic Prkcd-cre knock-in rat and characterized this model using anatomical, electrophysiological, and behavioral approaches in both sexes. In the CeA, Cre was selectively expressed in PKCδ+ cells. Anterograde projections of PKCδ+ neurons to cortical regions, subcortical regions, several hypothalamic nuclei, the amygdala complex, and midbrain dopaminergic regions were largely consistent with published mouse data. In a behavioral screen, we found no differences between Cre+ rats and Cre- wild-type littermates. Optogenetic stimulation of CeA PKCδ+ neurons in a palatable food intake assay resulted in an increased latency to first feeding and decreased total food intake, once again replicating published mouse findings. Lastly, using a real-time place preference task, we found that stimulation of PKCδ+ neurons promoted aversion, without affecting locomotor activity. Collectively, these findings establish the novel Prkcd-Cre rat line as a valuable tool that complements available mouse lines for investigating the functional role of PKCδ+ neurons.

An Update on Protein Kinases as Therapeutic Targets-Part I: Protein Kinase C Activation and Its Role in Cancer and Cardiovascular Diseases

Protein kinases are one of the most significant drug targets in the human proteome, historically harnessed for the treatment of cancer, cardiovascular disease, and a growing number of other conditions, including autoimmune and inflammatory processes. Since the approval of the first kinase inhibitors in the late 1990s and early 2000s, the field has grown exponentially, comprising 98 approved therapeutics to date, 37 of which were approved between 2016 and 2021. While many of these small-molecule protein kinase inhibitors that interact orthosterically with the protein kinase ATP binding pocket have been massively successful for oncological indications, their poor selectively for protein kinase isozymes have limited them due to toxicities in their application to other disease spaces. Thus, recent attention has turned to the use of alternative allosteric binding mechanisms and improved drug platforms such as modified peptides to design protein kinase modulators with enhanced selectivity and other pharmacological properties. Herein we review the role of different protein kinase C (PKC) isoforms in cancer and cardiovascular disease, with particular attention to PKC-family inhibitors. We discuss translational examples and carefully consider the advantages and limitations of each compound (Part I). We also discuss the recent advances in the field of protein kinase modulators, leverage molecular docking to model inhibitor-kinase interactions, and propose mechanisms of action that will aid in the design of next-generation protein kinase modulators (Part II).

Protein Kinase C Regulates Expression and Function of the Cav3.2 T-Type Ca2+ Channel during Maturation of Neonatal Rat Cardiomyocyte

Two distinct isoforms of the T-type Ca2+ channel, Cav3.1 and Cav3.2, play a pivotal role in the generation of pacemaker potentials in nodal cells in the heart, although the isoform switches from Cav3.2 to Cav3.1 during the early neonatal period with an unknown mechanism. The present study was designed to investigate the molecular system of the parts that are responsible for the changes of T-type Ca2+ channel isoforms in neonatal cardiomyocytes using the whole-cell patch-clamp technique and mRNA quantification. The present study demonstrates that PKC activation accelerates the Ni2+-sensitive beating rate and upregulates the Ni2+-sensitive T-type Ca2+ channel current in neonatal cardiomyocytes as a long-term effect, whereas PKC inhibition delays the Ni2+-sensitive beating rate and downregulates the Ni2+-sensitive T-type Ca2+ channel current. Because the Ni2+-sensitive T-type Ca2+ channel current is largely composed of the Cav3.2-T-type Ca2+ channel, it is accordingly assumed that PKC activity plays a crucial role in the maintenance of the Cav3.2 channel. The expression of Cav3.2 mRNA was highly positively correlated with PKC activity. The expression of a transcription factor Nkx2.5 mRNA, possibly corresponding to the Cav3.2 channel gene, was decreased by an inhibition of PKCβII. These results suggest that PKC activation, presumably by PKCβII, is responsible for the upregulation of CaV3.2 T-type Ca2+ channel expression that interacts with a cardiac-specific transcription factor, Nkx2.5, in neonatal cardiomyocytes.

Protein Kinase C-Mediated Hyperphosphorylation and Lateralization of Connexin 43 Are Involved in Autoimmune Myocarditis-Induced Prolongation of QRS Complex

Myocarditis is a serious and potentially life-threatening disease, which leads to cardiac dysfunction and sudden cardiac death. An increasing number of evidence suggests that myocarditis is also a malignant complication of coronavirus pneumonia, associated with heart failure and sudden cardiac death. Prolonged QRS complexes that are related to malignant arrhythmias caused by myocarditis significantly increase the risk of sudden cardiac death in patients. However, the molecular mechanisms are not fully known at present. In this study, we identify protein kinase C (PKC) as a new regulator of the QRS complex. In isolated hearts of normal rats, the PKC agonist, phorbol-12-myristate-13-acetate (PMA), induced prolongation of the QRS complex. Mechanistically, hyperphosphorylation and lateralization of connexin 43 (Cx43) by PKC induced depolymerization and internalization of Cx43 gap junction channels and prolongation of the QRS duration. Conversely, administration of the PKC inhibitor, Ro-32-0432, in experimental autoimmune myocarditis (EAM) rats after the most severe inflammation period still significantly rescued the stability of the Cx43 gap junction and alleviated prolongation of the QRS complex. Ro-32-0432 reduced phosphorylation and blocked translocation of Cx43 in EAM rat heart but did not regulate the mRNA expression level of ventricular ion channels and the other regulatory proteins, which indicates that the inhibition of PKC might have no protective effect on ion channels that generate ventricular action potential in EAM rats. These results suggest that the pharmacological inhibition of PKC ameliorates the prolongation of the QRS complex via suppression of Cx43 hyperphosphorylation, lateralization, and depolymerization of Cx43 gap junction channels in EAM rats, which provides a potential therapeutic strategy for myocarditis-induced arrhythmias.

Myofilament Phosphorylation in Stem Cell Treated Diastolic Heart Failure

RATIONALE

Phosphorylation of sarcomeric proteins has been implicated in heart failure with preserved ejection fraction (HFpEF); such changes may contribute to diastolic dysfunction by altering contractility, cardiac stiffness, Ca²⁺-sensitivity, and mechanosensing. Treatment with cardiosphere-derived cells (CDCs) restores normal diastolic function, attenuates fibrosis and inflammation, and improves survival in a rat HFpEF model.

OBJECTIVE

Phosphorylation changes that underlie HFpEF and those reversed by CDC therapy, with a focus on the sarcomeric subproteome were analyzed.

METHODS AND RESULTS

Dahl salt-sensitive rats fed a high-salt diet, with echocardiographically verified diastolic dysfunction, were randomly assigned to either intracoronary CDCs or placebo. Dahl salt-sensitive rats receiving low salt diet served as controls. Protein and phosphorylated Ser, Thr, and Tyr residues from left ventricular tissue were quantified by mass spectrometry. HFpEF hearts exhibited extensive hyperphosphorylation with 98% of the 529 significantly changed phospho-sites increased compared with control. Of those, 39% were located within the sarcomeric subproteome, with a large group of proteins located or associated with the Z-disk. CDC treatment partially reverted the hyperphosphorylation, with 85% of the significantly altered 76 residues hypophosphorylated. Bioinformatic upstream analysis of the differentially phosphorylated protein residues revealed PKC as the dominant putative regulatory kinase. PKC isoform analysis indicated increases in PKC α, β, and δ concentration, whereas CDC treatment led to a reversion of PKCβ. Use of PKC isoform specific inhibition and overexpression of various PKC isoforms strongly suggests that PKCβ is the dominant kinase involved in hyperphosphorylation in HFpEF and is altered with CDC treatment.

CONCLUSIONS

Increased protein phosphorylation at the Z-disk is associated with diastolic dysfunction, with PKC isoforms driving most quantified phosphorylation changes. Because CDCs reverse the key abnormalities in HFpEF and selectively reverse PKCβ upregulation, PKCβ merits being classified as a potential therapeutic target in HFpEF, a disease notoriously refractory to medical intervention.

Putative role of natural products as Protein Kinase C modulator in different disease conditions

INTRODUCTION

Protein kinase C (PKC) is a promising drug target for various therapeutic areas. Natural products derived from plants, animals, microorganisms, and marine organisms have been used by humans as medicine from prehistoric times. Recently, several compounds derived from plants have been found to modulate PKC activities through competitive binding with ATP binding site, and other allosteric regions of PKC. As a result fresh race has been started in academia and pharmaceutical companies to develop an effective naturally derived small-molecule inhibitor to target PKC activities. Herein, in this review, we have discussed several natural products and their derivatives, which are reported to have an impact on PKC signaling cascade.

METHODS

All information presented in this review article regarding the regulation of PKC by natural products has been acquired by a systematic search of various electronic databases, including ScienceDirect, Scopus, Google Scholar, Web of science, ResearchGate, and PubMed. The keywords PKC, natural products, curcumin, rottlerin, quercetin, ellagic acid, epigallocatechin-3 gallate, ingenol 3 angelate, resveratrol, protocatechuic acid, tannic acid, PKC modulators from marine organism, bryostatin, staurosporine, midostaurin, sangivamycin, and other relevant key words were explored.

RESULTS

The natural products and their derivatives including curcumin, rottlerin, quercetin, ellagic acid, epigallocatechin-3 gallate, ingenol 3 angelate, resveratrol, bryostatin, staurosporine, and midostaurin play a major role in the management of PKC activity during various disease progression.

CONCLUSION

Based on the comprehensive literature survey, it could be concluded that various natural products can regulate PKC activity during disease progression. However, extensive research is needed to circumvent the challenge of isoform specific regulation of PKC by natural products.

Intra-Cellular Calcium Signaling Pathways (PKC, RAS/RAF/MAPK, PI3K) in Lamina Cribrosa Cells in Glaucoma

The lamina cribrosa (LC) is a key site of fibrotic damage in glaucomatous optic neuropathy and the precise mechanisms of LC change remain unclear. Elevated Ca²⁺ is a major driver of fibrosis, and therefore intracellular Ca²⁺ signaling pathways are relevant glaucoma-related mechanisms that need to be studied. Protein kinase C (PKC), mitogen-activated MAPK kinases (p38 and p42/44-MAPK), and the PI3K/mTOR axis are key Ca²⁺ signal transducers in fibrosis and we therefore investigated their expression and activity in normal and glaucoma cultured LC cells. We show, using Western immune-blotting, that hyposmotic-induced cellular swelling activates PKCα, p42/p44, and p38 MAPKs, the activity is transient and biphasic as it peaks between 2 min and 10 min. The expression and activity of PKCα, p38 and p42/p44-MAPKs are significantly (p < 0.05) increased in glaucoma LC cells at basal level, and at different time-points after hyposmotic stretch. We also found elevated mRNA expression of mRNA expression of PI3K, IP3R, mTOR, and CaMKII in glaucoma LC cells. This study has identified abnormalities in multiple calcium signaling pathways (PKCα, MAPK, PI3K) in glaucoma LC cells, which might have significant functional and therapeutic implications in optic nerve head (ONH) fibrosis and cupping in glaucoma.

Attenuation of amyloid-β generation by atypical protein kinase C-mediated phosphorylation of engulfment adaptor PTB domain containing 1 threonine 35

Amyloid-β (Aβ) is derived from the proteolytic processing of amyloid precursor protein (APP), and the deposition of extracellular Aβ to form amyloid plaques is a pathologic hallmark of Alzheimer's disease (AD). Although reducing Aβ generation and accumulation has been proposed as a means of treating the disease, adverse side effects and unsatisfactory efficacy have been reported in several clinical trials that sought to lower Aβ levels. Engulfment adaptor phosphotyrosine-binding (PTB) domain containing 1 (GULP1) is a molecular adaptor that has been shown to interact with APP to alter Aβ production. Therefore, the modulation of the GULP1-APP interaction may be an alternative approach to reducing Aβ. However, the mechanisms that regulate GULP1-APP binding remain elusive. As GULP1 is a phosphoprotein, and because phosphorylation is a common mechanism that regulates protein interaction, we anticipated that GULP1 phosphorylation would influence GULP1-APP interaction and thereby Aβ production. We show here that the phosphorylation of GULP1 threonine 35 (T35) reduces GULP1-APP interaction and suppresses the stimulatory effect of GULP1 on APP processing. The residue is phosphorylated by an isoform of atypical PKC (PKCζ). Overexpression of PKCζ reduces both GULP1-APP interaction and GULP1-mediated Aβ generation. Moreover, the activation of PKCζ via insulin suppresses APP processing. In contrast, GULP1-mediated APP processing is enhanced in PKCζ knockout cells. Similarly, PKC ι, another member of atypical PKC, also decreases GULP1-mediated APP processing. Intriguingly, our X-ray crystal structure of GULP1 PTB-APP intracellular domain (AICD) peptide reveals that GULP1 T35 is not located at the GULP1-AICD binding interface; rather, it immediately precedes the β1-α2 loop that forms a portion of the binding groove for the APP helix αC. Phosphorylating the residue may induce an allosteric effect on the conformation of the binding groove. Our results indicate that GULP1 T35 phosphorylation is a mechanism for the regulation of GULP1-APP interaction and thereby APP processing. Moreover, the activation of atypical PKC, such as by insulin, may confer a beneficial effect on AD by lowering GULP1-mediated Aβ production.-Chau, D. D.-L., Yung, K. W.-Y., Chan, W. W.-L., An, Y., Hao, Y., Chan, H.-Y. E., Ngo, J. C.-K., Lau, K.-F. Attenuation of amyloid-β generation by atypical protein kinase C-mediated phosphorylation of engulfment adaptor PTB domain containing 1 threonine 35.

Protein kinase C and cardiac dysfunction: a review

Heart failure (HF) is a physiological state in which cardiac output is insufficient to meet the needs of the body. It is a clinical syndrome characterized by impaired ability of the left ventricle to either fill or eject blood efficiently. HF is a disease of multiple aetiologies leading to progressive cardiac dysfunction and it is the leading cause of deaths in both developed and developing countries. HF is responsible for about 73,000 deaths in the UK each year. In the USA, HF affects 5.8 million people and 550,000 new cases are diagnosed annually. Cardiac remodelling (CD), which plays an important role in pathogenesis of HF, is viewed as stress response to an index event such as myocardial ischaemia or imposition of mechanical load leading to a series of structural and functional changes in the viable myocardium. Protein kinase C (PKC) isozymes are a family of serine/threonine kinases. PKC is a central enzyme in the regulation of growth, hypertrophy, and mediators of signal transduction pathways. In response to circulating hormones, activation of PKC triggers a multitude of intracellular events influencing multiple physiological processes in the heart, including heart rate, contraction, and relaxation. Recent research implicates PKC activation in the pathophysiology of a number of cardiovascular disease states. Few reports are available that examine PKC in normal and diseased human hearts. This review describes the structure, functions, and distribution of PKCs in the healthy and diseased heart with emphasis on the human heart and, also importantly, their regulation in heart failure.

Protein Kinase C Inhibition With Ruboxistaurin Increases Contractility and Reduces Heart Size in a Swine Model of Heart Failure With Reduced Ejection Fraction

Inotropic support is often required to stabilize the hemodynamics of patients with acute decompensated heart failure; while efficacious, it has a history of leading to lethal arrhythmias and/or exacerbating contractile and energetic insufficiencies. Novel therapeutics that can improve contractility independent of beta-adrenergic and protein kinase A-regulated signaling, should be therapeutically beneficial. This study demonstrates that acute protein kinase C-α/β inhibition, with ruboxistaurin at 3 months' post-myocardial infarction, significantly increases contractility and reduces the end-diastolic/end-systolic volumes, documenting beneficial remodeling. These data suggest that ruboxistaurin represents a potential novel therapeutic for heart failure patients, as a moderate inotrope or therapeutic, which leads to beneficial ventricular remodeling.

Influenza virus recruits host protein kinase C to control assembly and activity of its replication machinery

Influenza virus expresses transcripts early in infection and transitions towards genome replication at later time points. This process requires de novo assembly of the viral replication machinery, large ribonucleoprotein complexes (RNPs) composed of the viral polymerase, genomic RNA and oligomeric nucleoprotein (NP). Despite the central role of RNPs during infection, the factors dictating where and when they assemble are poorly understood. Here we demonstrate that human protein kinase C (PKC) family members regulate RNP assembly. Activated PKCδ interacts with the polymerase subunit PB2 and phospho-regulates NP oligomerization and RNP assembly during infection. Consistent with its role in regulating RNP assembly, knockout of PKCδ impairs virus infection by selectively disrupting genome replication. However, primary transcription from pre-formed RNPs deposited by infecting particles is unaffected. Thus, influenza virus exploits host PKCs to regulate RNP assembly, a step required for the transition from primary transcription to genome replication during the infectious cycle.

Polyphenol compounds and PKC signaling

BACKGROUND

Naturally occurring polyphenols found in food sources provide huge health benefits. Several polyphenolic compounds are implicated in the prevention of disease states, such as cancer. One of the mechanisms by which polyphenols exert their biological actions is by interfering in the protein kinase C (PKC) signaling pathways. PKC belongs to a superfamily of serine-threonine kinase and are primarily involved in phosphorylation of target proteins controlling activation and inhibition of many cellular processes directly or indirectly.

SCOPE OF REVIEW

Despite the availability of substantial literature data on polyphenols' regulation of PKC, no comprehensive review article is currently available on this subject. This article reviews PKC-polyphenol interactions and its relevance to various disease states. In particular, salient features of polyphenols, PKC, interactions of naturally occurring polyphenols with PKC, and future perspective of research on this subject are discussed.

MAJOR CONCLUSIONS

Some polyphenols exert their antioxidant properties by regulating the transcription of the antioxidant enzyme genes through PKC signaling. Regulation of PKC by polyphenols is isoform dependent. The activation or inhibition of PKC by polyphenols has been found to be dependent on the presence of membrane, Ca(2+) ion, cofactors, cell and tissue types etc. Two polyphenols, curcumin and resveratrol are in clinical trials for the treatment of colon cancer.

GENERAL SIGNIFICANCE

The fact that 74% of the cancer drugs are derived from natural sources, naturally occurring polyphenols or its simple analogs with improved bioavailability may have the potential to be cancer drugs in the future.

Histone hyperacetylation up-regulates protein kinase Cδ in dopaminergic neurons to induce cell death: relevance to epigenetic mechanisms of neurodegeneration in Parkinson disease

The oxidative stress-sensitive protein kinase Cδ (PKCδ) has been implicated in dopaminergic neuronal cell death. However, little is known about the epigenetic mechanisms regulating PKCδ expression in neurons. Here, we report a novel mechanism by which the PKCδ gene can be regulated by histone acetylation. Treatment with histone deacetylase (HDAC) inhibitor sodium butyrate (NaBu) induced PKCδ expression in cultured neurons, brain slices, and animal models. Several other HDAC inhibitors also mimicked NaBu. The chromatin immunoprecipitation analysis revealed that hyperacetylation of histone H4 by NaBu is associated with the PKCδ promoter. Deletion analysis of the PKCδ promoter mapped the NaBu-responsive element to an 81-bp minimal promoter region. Detailed mutagenesis studies within this region revealed that four GC boxes conferred hyperacetylation-induced PKCδ promoter activation. Cotransfection experiments and Sp inhibitor studies demonstrated that Sp1, Sp3, and Sp4 regulated NaBu-induced PKCδ up-regulation. However, NaBu did not alter the DNA binding activities of Sp proteins or their expression. Interestingly, a one-hybrid analysis revealed that NaBu enhanced transcriptional activity of Sp1/Sp3. Overexpression of the p300/cAMP-response element-binding protein-binding protein (CBP) potentiated the NaBu-mediated transactivation potential of Sp1/Sp3, but expressing several HDACs attenuated this effect, suggesting that p300/CBP and HDACs act as coactivators or corepressors in histone acetylation-induced PKCδ up-regulation. Finally, using genetic and pharmacological approaches, we showed that NaBu up-regulation of PKCδ sensitizes neurons to cell death in a human dopaminergic cell model and brain slice cultures. Together, these results indicate that histone acetylation regulates PKCδ expression to augment nigrostriatal dopaminergic cell death, which could contribute to the progressive neuropathogenesis of Parkinson disease.

Ginsenoside Re rescues methamphetamine-induced oxidative damage, mitochondrial dysfunction, microglial activation, and dopaminergic degeneration by inhibiting the protein kinase Cδ gene

Ginsenoside Re, one of the main constituents of Panax ginseng, possesses novel antioxidant and anti-inflammatory properties. However, the pharmacological mechanism of ginsenoside Re in dopaminergic degeneration remains elusive. We suggested that protein kinase C (PKC) δ mediates methamphetamine (MA)-induced dopaminergic toxicity. Treatment with ginsenoside Re significantly attenuated methamphetamine-induced dopaminergic degeneration in vivo by inhibiting impaired enzymatic antioxidant systems, mitochondrial oxidative stress, mitochondrial translocation of protein kinase Cδ, mitochondrial dysfunction, pro-inflammatory microglial activation, and apoptosis. These protective effects were comparable to those observed with genetic inhibition of PKCδ in PKCδ knockout (-/-) mice and with PKCδ antisense oligonucleotides, and ginsenoside Re did not provide any additional protective effects in the presence of PKCδ inhibition. Our results suggest that PKCδ is a critical target for ginsenoside Re-mediated protective activity in response to dopaminergic degeneration induced by MA.

Protein kinase C delta mediated cytotoxicity of 6-Hydroxydopamine via sustained extracellular signal-regulated kinase 1/2 activation in PC12 cells

OBJECTIVES

The incidence of Parkinson's disease (PD) is increasing as the global population ages. 6-hydroxydopamine (6-OHDA) can induce PD-like neuropathology and biochemical changes in both in vitro and in vivo models. Therefore, clarification of the molecular mechanism of 6-OHDA-induced cell death might contribute to the understanding of the pathogenesis of PD.

METHODS

With this goal in mind, we investigated the role of protein kinase C delta (PKC delta) in 6-OHDA-dependent death using the pheochromocytoma cell line, PC12. Cells were treated with 6-OHDA to induce toxicity with or without pretreatment using rottlerin (a PKC delta inhibitor), bisindolylmaleimide I (a general PKC inhibitor), Gö6976 (a PKC inhibitor selective for calcium-dependent PKC isoforms), or phorbol-12-myristate-13-acetate (PMA, a PKC activator).

RESULTS

Phorbol-12-myristate-13-acetate decreased cell survival and increased the rate of apoptosis while rottlerin increased cell survival and decreased the rate of apoptosis. In contrast, neither bisindolylmaleimide I nor Gö6976 affected 6-OHDA-induced cell death. Western analysis demonstrated that phosphorylation of PKC delta on Thr 505 as well as extracellular signal-regulated kinase (ERK) phosphorylation increased after exposure to 6-OHDA. This increase in PKC delta phosphorylation was potentiated by PMA. However, rottlerin attenuated the 6-OHDA-stimulated increase in PKC delta and ERK phosphorylation.

CONCLUSION

These data suggest that PKC delta, rather than classic-type PKC (alpha, beta1, beta2, gamma), participates in 6-OHDA-induced neurotoxicity in PC12 cells, and PKC delta activity is required for subsequent ERK activation during cell death.

Baicalein, isolated from Scutellaria baicalensis, protects against endothelin-1-induced pulmonary artery smooth muscle cell proliferation via inhibition of TRPC1 channel expression

ETHNOPHARMACOLOGICAL RELEVANCE

We investigated the antiproliferative effects of baicalein, isolated from Scutellaria baicalensis (Huang-qin), on ET-1-mediated pulmonary artery smooth muscle cells (PASMCs) proliferation and the mechanisms underlying these effects.

MATERIALS AND METHODS

Intrapulmonary artery smooth muscle cells were isolated and cultured from female Sprague-Dawley rats and used during passages 3-6. The proliferation of PASMCs was quantified by cell counting and XTT assay. The protein expression of TRPC1 and PKCα were determined by western blotting. The cell cycle pattern was assayed by flow cytometry. The intracellular calcium concentrations ([Ca(2+)](i)) were measured using the fluorescent indicator fura-2-AM and flow cytometry.

RESULTS

Baicalein (0.3-3 μM) inhibited PASMCs proliferation, promoted cell cycle progression, enhanced [Ca(2+)](i) levels, increased capacitative Ca(2+) entry (CCE), upregulated the canonical transient receptor potential 1 (TRPC1) channel and membrane protein kinase Cα (PKCα) expression induced by ET-1 (0.1 μM). The PKC activator PMA (1 μM) reversed the inhibitory effects of baicalein on ET-1-induced upregulation of TRPC1 expression and S phase accumulation, while the PKC inhibitor chelerythrine (1 μM) potentiated baicalein-mediated G(2)/M phase arrest and TRPC1 channel inhibition.

CONCLUSION

Our findings suggest that baicalein protects against ET-1-induced PASMCs proliferation via modulation of the PKC-mediated TRPC channel.

Protein kinase Cα as a heart failure therapeutic target

Heart failure afflicts ~5 million people and causes ~300,000 deaths a year in the United States alone. Heart failure is defined as a deficiency in the ability of the heart to pump sufficient blood in response to systemic demands, which results in fatigue, dyspnea, and/or edema. Identifying new therapeutic targets is a major focus of current research in the field. We and others have identified critical roles for protein kinase C (PKC) family members in programming aspects of heart failure pathogenesis. More specifically, mechanistic data have emerged over the past 6-7 years that directly implicate PKCα, a conventional PKC family member, as a nodal regulator of heart failure propensity. Indeed, deletion of the PKCα gene in mice, or its inhibition in rodents with drugs or a dominant negative mutant and/or inhibitory peptide, has shown dramatic protective effects that antagonize the development of heart failure. This review will weigh all the evidence implicating PKCα as a novel therapeutic target to consider for the treatment of heart failure. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."

Disruption of astrocytic glutamine turnover by manganese is mediated by the protein kinase C pathway

Manganese (Mn) is a trace element essential for normal human development and is required for the proper functioning of a variety of physiological processes. Chronic exposure to Mn can cause manganism, a neurodegenerative disorder resembling idiopathic Parkinson's disease (PD). Mn(II) neurotoxicity is characterized by astrocytic impairment both in the expression and activity of glutamine (Gln) transporters. Because protein kinase C (PKC) activation leads to the downregulation of a number of neurotransmitter transporters and Mn(II) increases PKC activity, we hypothesized that the PKC signaling pathway contributes to the Mn(II)-mediated disruption of Gln turnover. Our results have shown that Mn exposure increases the phosphorylation of both the PKCα and PKCδ isoforms. PKC activity was also shown to be increased in response to Mn(II) treatment. Corroborating our earlier observations, Mn(II) also caused a decrease in Gln uptake. This effect was blocked by PKC inhibitors. Notably, PKC activation caused a decrease in Gln uptake mediated by systems ASC and N, but had no effect on the activities of systems A and L. Exposure to α-phorbol 12-myristate 13-acetate significantly decreased SNAT3 (system N) and ASCT2 (system ASC) protein levels. Additionally, a co-immunoprecipitation study demonstrated the association of SNAT3 and ASCT2 with the PKCδ isoform, and Western blotting revealed the Mn(II)-mediated activation of PKCδ by proteolytic cleavage. PKC activation was also found to increase SNAT3 and ubiquitin ligase Nedd4-2 binding and to induce hyperubiquitination. Taken together, these findings demonstrate that the Mn(II)-induced dysregulation of Gln homeostasis in astrocytes involves PKCδ signaling accompanied by an increase in ubiquitin-mediated proteolysis.

Plasma membrane Ca2+-ATPases in the nervous system during development and ageing

Calcium signaling is used by neurons to control a variety of functions, including cellular differentiation, synaptic maturation, neurotransmitter release, intracellular signaling and cell death. This review focuses on one of the most important Ca²⁺ regulators in the cell, the plasma membrane Ca²⁺-ATPase (PMCA), which has a high affinity for Ca²⁺ and is widely expressed in brain. The ontogeny of PMCA isoforms, linked to specific requirements of Ca²⁺ during development of different brain areas, is addressed, as well as their function in the adult tissue. This is based on the high diversity of variants in the PMCA family in brain, which show particular kinetic differences possibly related to specific localizations and functions of the cell. Conversely, alterations in the activity of PMCAs could lead to changes in Ca²⁺ homeostasis and, consequently, to neural dysfunction. The involvement of PMCA isoforms in certain neuropathologies and in brain ageing is also discussed.

Regulation of tumor suppressor PDCD4 by novel protein kinase C isoforms

Transforming growth factor-beta1 (TGF-beta1) induces apoptosis in normal hepatocytes and hepatoma cells. PDCD4 is involved in TGF-beta1-induced apoptosis via the Smad pathway. The tumor promoter 12-O-tetradecanoylphorbor-13-acetate (TPA), a protein kinase C stimulator, inhibits TGF-beta1-induced apoptosis. However, the mechanisms of TPA action on PDCD4 expression remain to be elucidated. Therefore. the regulatory mechanism of PDCD4 expression by PKC was investigated. The treatment of the human hepatoma cell line, Huh7 with TPA suppressed PDCD4 protein expression and TGF-beta1 failed to increase the PDCD4 protein expression. PKC inhibitors Ro-31-8425 or bisindolylmaleimide-1-hydrocholoride (pan-PKC inhibitors) and rottlerin (PKCdelta inhibitor), but not Go6976 (PKCalpha inhibitor), enhanced the induction of PDCD4 protein by TGF-beta1. Furthermore, siRNA-mediated knockdown of PKCdelta and epsilon, but not PKCalpha, augmented the TGF-beta1-stimulated PDCD4 protein expression. However, TPA or pan-PKC inhibitor did not alter the PDCD4 mRNA expression either under basal- and TGF-beta1-treated conditions. The down-regulation of PDCD4 by TPA was restored by treatment with the proteasome inhibitor MG132. These data suggest that two isoforms of PKCs are involved in the regulation of the PDCD4 protein expression related to the proteasomal degradation pathway.

Inhibition of protein kinase C phosphorylation of hepatitis B virus capsids inhibits virion formation and causes intracellular capsid accumulation

Capsids of hepatitis B virus and other hepadnaviruses contain a cellular protein kinase, which phosphorylates the capsid protein. Some phosphorylation sites are shown to be essential for distinct steps of viral replication as pregenome packaging or plus strand DNA synthesis. Although different protein kinases have been reported to phosphorylate the capsid protein, varying experimental approaches do not allow direct comparison. Furthermore, the activity of a specific protein kinase has not yet been correlated to steps in the hepadnaviral life cycle. In this study we show that capsids from various sources encapsidate active protein kinase Calpha, irrespective of hepatitis B virus genotype and host cell. Treatment of a virion expressing cell line with a pseudosubstrate inhibitor showed that inhibition of protein kinase C phosphorylation did not affect genome maturation but resulted in capsid accumulation and inhibited virion release to the medium. Our results imply that different protein kinases have distinct functions within the hepadnaviral life cycle.

Androgens induce dopaminergic neurotoxicity via caspase-3-dependent activation of protein kinase Cdelta

Aged men have a greater incidence of Parkinson's disease (PD) than women. PD is a neurodegenerative condition associated with the loss of dopamine neurons in the nigrostriatal pathway. This study examined the neurotoxic effects of androgens in a dopaminergic cell line (N27 cells) and the downstream signaling pathways activated by androgens. Treatment of N27 cells with testosterone- and dihydrotestosterone-induced mitochondrial dysfunction, protein kinase C (PKC)-delta cleavage, and apoptosis in dopaminergic neuronal cells. Inhibition of caspase-3 prevented the cleavage of PKCdelta from the full-length element to the catalytic fragment and apoptosis in N27 cells, suggesting that androgen-induced apoptosis is mediated by caspase-3-dependent activation of PKCdelta. Androgen-induced apoptosis may be specific to dopamine neurons as evidenced by a lack of testosterone-induced apoptosis in GnRH neurons. These results support a neurotoxic consequence of testosterone on dopaminergic neurons and may provide insight into the gender bias found in PD.

Rottlerin protected dopaminergic cell line from cytotoxicity of 6-hydroxydopamine by inhibiting PKCdelta phosphorylation

OBJECTIVE

The present study aims to investigate the role of protein kinase C delta subtype (PKCdelta) phosphorylation in the process of 6-hydroxydopamine (6-OHDA)-induced dopaminergic cell death, and demonstrate the molecular basis of neurological disorders, such as Parkinson's disease.

METHODS

The pheochromocytoma (PC12) cell line was employed in the present study. Cells were treated with 2 mumol/L PKCdelta inhibitor Rottlerin, 10 nmol/L protein kinase C delta subtype (PKCdelta) inhibitor bisindolylmaleimide I, or 5 nmol/L Gö6976 that could specifically inhibit the calcium-dependent PKCdelta isoforms, respectively. PKC activator phorbol-12-myristate-13-acetate (PMA, 100 nmol/L) was also used in this study. All these agents were added to the medium before cells were incubated with 6-OHDA. Cells with no treatment served as control. The cytotoxicity of 6-OHDA was determined by methyl thiazolyl tetrazolium (MTT) reduction assay and PKCdelta phosphorylation levels in various groups were measured by western blotting.

RESULTS

Bisindolylmaleimide I and Gö6976 exerted no significant attenuation on the cytotoxicity of 6-OHDA, nor any effects on PKCdelta phosphorylation in PC12 cells. However, Rottlerin could inhibit the phosphorylation of PKCdelta and attenuate 6-OHDA-induced cell death, and the cell viability was raised to (69.6+/-2.63)% of that in control group (P<0.05). In contrast, PMA induced a significant increase in PKCdelta phosphorylation and also strengthened the cytotoxic effects of 6-OHDA. The cell viability of PMA-treated PC12 cells decreased to (49.8+/-5.06)% of that in control group (P<0.001).

CONCLUSION

Rottlerin can protect PC12 cells from cytotoxicity of 6-OHDA probably by inhibiting PKCdelta phosphorylation. The results suggest that PKCdelta may be a key regulator of neuron loss in Parkinson's disease.

Expression and localization of atypical PKC isoforms in liver parenchymal cells

Members of all three classes of the protein kinase C (PKC) family including atypical PKCzeta (PKCzeta) are involved in central functions of liver parenchymal cells. However, expression and localization of PKCiota (PKCiota), the highly homologous atypical PKC (aPKC) isoform, in hepatocytes is unknown to date. PKCzeta and PKCiota were cloned from human and rat liver and fused to fluorescent protein tags (YFP). The sequence of full-length rat PKCiota is not yet known and was cloned from cDNA of hepatocytes by the use of degenerated primers. PKCzeta-YFP and PKCiota-YFP (human and rat) were expressed in HeLa or HEK293 cells and used to test the specificity of seven aPKC antibodies. Two antibodies were PKCiota-specific and two were specific for PKCzeta in immunofluorescence and Western blot analysis. Subcellular localization was analyzed by immunofluorescence in isolated rat and human hepatocytes and liver sections. Low immunoreactivity for aPKCs was found at the sinusoidal membrane and in the cytosol. The highest density of PKCiota as well as PKCzeta was found at the canalicular membrane in co-localization with ABC-transporters, such as bile salt export pump or multidrug resistance-associated protein 2. This topology suggests a specific function of aPKCs at the canalicular membrane in addition to their known role in cell polarity of epithelial cells.

Differentiation-Associated Expression of Conventional Protein Kinase C Isoforms in Primary Cultures of Bone Marrow Cells Induced by M-CSF and G-CSF

The Protein kinase C (PKC) -associated signal pathway plays crucial roles in regulation of cell growth, differentiation and apoptosis. The present study focuses on conventional PKC (cPKC) expression and its regulation in primary cultures of bone marrow cells induced to undergo macrophage/granulocyte differentiation by macrophage colony-stimulating factor (M-CSF) or granular colony-stimulating factor (G-CSF). By performing western blot analysis with pan anti-PKC antibodies, we found that PKC is transiently induced by M-CSF, reaching a maximum level by day 2, and then declines and diminishes by day 9 in primary culture of bone marrow cells. In contrast, the expression of PKC along G-CSF induced granulocytic differentiation of bone marrow stem cells is low and increases gradually. Reverse transcription-PCR (RT-PCR) assay was utilized to investigate the expression of PKC isoforms. PKC-alpha is constitutively expressed in bone marrow cells independently of hematopoietic growth factors in cultures. PKC-gamma mRNA is undetectable. Similarly, the expression of PKC-beta is transiently induced by M-CSF, yet steadily increased by G-CSF, in agreement with results obtained from PKC protein expression. Furthermore, gel-shift assay showed that the activation of NF-kappaB is transiently induced by M-CSF but not by G-CSF. These data suggest that PKC expression is involved in both macrophage and granulocyte differentiation by bone marrow committed stem cells. Yet, NF-kappaB activation is only detected in macrophage and not granulocyte differentiation. Thus, we conclude that the PKC-mediated signaling pathway is distinctly involved in bone-marrow cell differentiation induced by M-CSF and G-CSF.

PKC isozymes in chronic cardiac disease: possible therapeutic targets?

Cardiovascular disease is the leading cause of death in the United States. Therefore, identifying therapeutic targets is a major focus of current research. Protein kinase C (PKC), a family of serine/threonine kinases, has been identified as playing a role in many of the pathologies of heart disease. However, the lack of specific PKC regulators and the ubiquitous expression and normal physiological functions of the 11 PKC isozymes has made drug development a challenge. Here we discuss the validity of therapeutically targeting PKC, an intracellular signaling enzyme. We describe PKC structure, function, and distribution in the healthy and diseased heart, as well as the development of rationally designed isozyme-selective regulators of PKC functions. The review focuses on the roles of specific PKC isozymes in atherosclerosis, fibrosis, and cardiac hypertrophy, and examines principles of pharmacology as they pertain to regulators of signaling cascades associated with these diseases.

6-hydroxydopamine-induced apoptosis is mediated via extracellular auto-oxidation and caspase 3-dependent activation of protein kinase Cdelta

6-Hydroxydopamine is a neurotoxin commonly used to lesion dopaminergic pathways and generate experimental models for Parkinson disease, however, the cellular mechanism of 6-hydroxydopamine-induced neurodegeneration is not well defined. In this study we have explored how 6-hydroxydopamine neurotoxicity is initiated. We have also investigated downstream signaling pathways activated in response to 6-hydroxydopamine, using a neuronal-like, catecholaminergic cell line (PC12 cells) as an in vitro model system. We have shown that 6-hydroxydopamine neurotoxicity is initiated via extracellular auto-oxidation and the induction of oxidative stress from the oxidative products generated. Neurotoxicity is completely attenuated by preincubation with catalase, suggesting that hydrogen peroxide, at least in part, evokes neuronal cell death in this model. 6-Hydroxydopamine does not initiate toxicity by dopamine transporter-mediated uptake into PC12 cells, because both GBR-12909 and nisoxetine (inhibitors of dopamine and noradrenaline transporters, respectively) failed to reduce toxicity. 6-Hydroxydopamine has previously been shown to induce both apoptotic and necrotic cell-death mechanisms. In this study oxidative stress initiated by 6-hydroxydopamine caused mitochondrial dysfunction, activation of caspases 3/7, nuclear fragmentation, and apoptosis. We have shown that, in this model, proteolytic activation of the proapoptotic protein kinase Cdelta (PKCdelta) is a key mediator of 6-hydroxydopamine-induced cell death. 6-Hydroxydopamine induces caspase 3-dependent cleavage of full-length PKCdelta (79 kDa) to yield a catalytic fragment (41 kDa). Inhibition of PKCdelta (with rottlerin or via RNA interference-mediated gene suppression) ameliorates the neurotoxicity evoked by 6-hydroxydopamine, implicating this kinase in 6-hydroxydopamine-induced neurotoxicity and Parkinsonian neurodegeneration.

A developmental profile of the levels of calcium pumps in chick cerebellum

The functional expression and distribution of intracellular ATPase (sarco(endo)plasmic reticulum Ca(2+)-ATPase: SERCA) and plasma membrane Ca(2+)-ATPase (PMCA) was analyzed in the developing chick cerebellum. The activity and Ca(2+) uptake increase with development for both ATPases. However, the protein content increases with the stage of development only for SERCA, remaining constant for PMCA. Immunohistochemical assays showed that the ontogenesis of these ATPases goes along with definite stages of cerebellum histogenesis, and is complete at hatching. The SERCA is mainly distributed in Purkinje neurons, whereas the PMCA seems to be expressed initially in climbing fibers, shifting to soma and spiny branchlets of Purkinje cells at late embryonic stages. Granule cells express both ATPases according to their degree of maturity, whereas only PMCA is present in cerebellar glomeruli. These pumps are present in deep nuclei and the choroid plexus, although in this latter tissue their expression declines with development. The spatio-temporal distribution of SERCA and PMCA must be closely related to their association with the development of specific cells and processes of the chick cerebellum.

Protein kinases in vascular smooth muscle tone--role in the pulmonary vasculature and hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is an adaptive mechanism that in the normal animal diverts blood away from poorly ventilated areas of the lung, thereby maintaining optimal ventilation-perfusion matching. In global hypoxia however, such as in respiratory disease or at altitude, it causes detrimental increases in pulmonary vascular resistance and pulmonary artery (PA) pressure. The precise intracellular pathways and mechanisms underlying HPV remain unclear, although it is now recognised that both an elevation in smooth muscle intracellular [Ca2+] and a concomitant increase in Ca2+ sensitivity are involved. Several key intracellular protein kinases have been proposed as components of the signal transduction pathways leading to development of HPV, specifically Rho kinase, non-receptor tyrosine kinases (NRTK), p38 mitogen activated protein (MAP) kinase, and protein kinase C (PKC). All of these have been implicated to a greater or lesser extent in pathways leading to Ca2+ sensitisation, and in some cases regulation of intracellular [Ca2+] as well. In this article, we review the role of these key protein kinases in the regulation of vascular smooth muscle (VSM) constriction, applying what is known in the systemic circulation to the pulmonary circulation and HPV. We conclude that the strongest evidence for direct involvement of protein kinases in the mechanisms of HPV concerns a central role for Rho kinase in Ca2+ sensitisation, and a potential role for Src-family kinases in both modulation of Ca2+ entry via capacitative Ca2+ entry (CCE) and activation of Rho kinase, though others are likely to have indirect or modulatory influences. In addition, we speculate that Src family kinases may provide a central interface between the proposed hypoxia-induced generation of reactive oxygen species by mitochondria and both the elevation in intracellular [Ca2+] and Rho kinase mediated Ca2+ sensitisation.

Selective decrease of membrane-associated PKC-alpha and PKC-epsilon in response to elevated intracellular O-GlcNAc levels in transformed human glial cells

Increased flux through the hexosamine biosynthetic pathway (HBP) has been shown to affect the activity and translocation of certain protein kinase C (PKC) isoforms. It has been suggested that this effect is due to increases in the beta-O-linked N-acetylglucosamine (O-GlcNAc) modification. Herein, we demonstrate the effect of increasing the O-GlcNAc modification on the translocation of select PKC isozymes in a human astroglial cell line. Treating cells with either 8 mM d-glucosamine (GlcN), 5 mM streptozotocin (STZ), or 80 muM O-(2-acetamido-2-deoxy-d-glucopyranosylidene)amino-N-phenylcarbamate (PUGNAc) produced a significant increase in the O-GlcNAc modification on both cytosolic and membrane proteins; however, both the level and rate of O-GlcNAc increase varied with the compound. GlcN treatment resulted in a rapid, transient translocation of PKC-betaII that was maximal after 3 h (73+/-8%) and also produced a 48+/-15% decrease in membrane-associated PKC-epsilon after 9 h of treatment. Similar to GlcN treatment, STZ and PUGNAc treatment also resulted in decreased levels of PKC-epsilon in the membrane fraction. Significant decreases were seen as early as 5 h and, by 9 h of treatment, had decreased by 87+/-6% with STZ and 73+/-7% with PUGNAc. Unlike GlcN, both STZ and PUGNAc produced a decrease in PKC-alpha membrane levels by 9 h posttreatment (78+/-10% with STZ and 66+/-8% with PUGNAc) while neither compound produced any changes in PKC-betaII translocation. In addition, none of the three compounds affected membrane levels of PKC-iota. Altogether, these results demonstrate a novel link between increased levels of the O-GlcNAc modification and the regulation of specific PKC isoforms.

Cell-specific role for epsilon- and betaI-protein kinase C isozymes in protecting cortical neurons and astrocytes from ischemia-like injury

Activation of epsilon protein kinase C (epsilonPKC) has been shown to protect cardiac myocytes against ischemia and reperfusion injury. However, the role of PKC in ischemic brain injury is less well defined. Western blot analysis of murine neurons and astrocytes in primary culture demonstrated epsilon- and betaIPKC expression in both cell types. Activation of epsilonPKC increased in neuronal cultures in response to the ischemia-like insult of oxygen-glucose deprivation (OGD). Isozyme-specific peptide activators or inhibitors of PKC were applied at various times before, during and after the OGD period. Neuron-astrocyte mixed cultures pretreated with a selective epsilonPKC activator peptide showed a significant reduction in neuronal injury after OGD and reperfusion, compared to cultures pretreated with control peptide. The epsilonPKC activator peptide counteracted the increased damage induced by pretreatment with the epsilonPKC-selective inhibitor peptide in relatively pure neuronal cultures subjected to OGD. Neither epsilonPKC activator nor inhibitor peptides affected injury of neurons when applied after OGD onset. In contrast, the betaIPKC-selective inhibitor peptide increased injury in astrocyte cultures exposed to OGD at all application times tested. Our data demonstrate protection of neurons by selective activation of epsilonPKC but enhanced astrocyte cell death with selective inhibition of betaIPKC. Thus PKC isozymes exhibit cell type-specific effects on ischemia-like injury.

Role of proteolytic activation of protein kinase Cdelta in oxidative stress-induced apoptosis

Protein kinase Cdelta (PKCdelta), a member of the novel PKC family, is emerging as a redox-sensitive kinase in various cell types. Oxidative stress activates the PKCdelta kinase by translocation, tyrosine phosphorylation, or proteolysis. During proteolysis, caspase-3 cleaves the native PKCdelta (72-74 kDa) into 41-kDa catalytically active and 38-kDa regulatory fragments to persistently activate the kinase. The proteolytic activation of PKCdelta plays a key role in promoting apoptotic cell death in various cell types, including neuronal cells. Attenuation of PKCdelta proteolytic activation by antioxidants suggests that the cellular redox status can influence activation of the proapoptotic kinase. PKCdelta may also amplify apoptotic signaling via positive feedback activation of the caspase cascade. Thus, the dual role of PKCdelta as a mediator and amplifier of apoptosis may be important in the pathogenesis of major neurodegenerative disorders, such as Parkinson's disease, Alzheimer's disease, and Huntington disease.

Protein kinase C activity, translocation, and selective isoform subcellular redistribution in the rat cerebral cortex after in vitro ischemia

Protein kinase C (PKC) involvement in ischemia-induced neuronal damage has been investigated in superfused rat cerebral cortex slices submitted to 15 min of oxygen-glucose deprivation (OGD) and in primary cultures of rat cortical neurons exposed to 100 microM glutamate (GLU) for 10 min. OGD significantly increased the total PKC activity in the slices, mostly translocated in the particulate fraction. After 1 hr of reperfusion, the total PKC activity was reduced and the translocated fraction dropped by 84% with respect to the control. Western blot analysis of OGD samples showed an increase in total beta(2) and epsilon PKC isoform levels. After reperfusion, the total levels of alpha, beta(1), beta(2) and gamma isoforms were significantly reduced, whereas the epsilon isoform remained at an increased level. Endogenous GLU release from OGD slices increased to about 15 times the basal values after 15 min of oxygen-glucose deprivation, and to 25 and 35 times the basal level in the presence of the PKC inhibitors staurosporine (0.1 microM) and bisindolylmaleimide (1 microM), respectively. Western blot analysis of GLU-treated cortical neurons showed a significant decrease only in the total level of beta(2) isoforms. Cell survival was reduced to 31% in GLU-treated neuronal cultures; PKC inhibitors were not able to modify this effect. These findings demonstrate that the cell response to OGD and GLU involves PKC in a complex way. The net role played by PKC during OGD may be to reduce GLU release and, consequently, neurotoxicity. The isoforms beta(2) and epsilon are affected the most and may play a significant role in the mechanisms underlying neurotoxicity/neuroprotection.

Inhibition of muscarinic receptor-induced proliferation of astroglial cells by ethanol: mechanisms and implications for the fetal alcohol syndrome

In utero exposure to ethanol is deleterious to fetal brain development. Children born with the fetal alcohol syndrome (FAS) display a number of abnormalities, the most significant of which are central nervous system (CNS) dysfunctions, such as microencephaly and mental retardation. An interaction of ethanol with glial cells, particularly astrocytes, has been suggested to contribute to the developmental neurotoxicity of this alcohol. At low concentrations (10-100 mM) ethanol inhibits the proliferation of astroglial cells in vitro, particularly when stimulated by acetycholine through muscarinic M3 receptors. Of the several signal transduction pathways activated by these receptors in astrocytes or astrocytoma cells, which are involved in mitogenic signaling, only some (e.g. protein kinase C (PKC) zeta, p70S6 kinase) appear to be targeted by ethanol at the same low concentrations which effectively inhibit proliferation. Inhibition of astroglial proliferation by ethanol may contribute to the microencephaly seen in FAS.

Alteration of protein kinase C isoforms in the liver of septic rat

The present study investigated the alteration of protein kinase C (PKC) isoforms in rat liver during the progression of sepsis. Cecal ligation and puncture (CLP) model of polymicrobial sepsis was used, with early and late sepsis referring to those animals sacrificed at 9 and 18 h, respectively, after CLP. The protein contents of various PKC isoforms were quantified by Western blot and densitometric analysis. PKCalpha activity was performed after immunoprecipitation and assayed based on the incorporation rate of 32p from [gamma-32p] adenosine triphosphate (ATP) into histone. The distribution of PKCalpha was evaluated by immunohistochemical staining. The steady state expression of PKCalpha mRNA was estimated by reverse transcriptase-polymerase chain reaction (RT-PCR). The results indicated that 1) five isoforms (alpha, beta, delta, epsilon, zeta) could be detected in normal rat liver. PKCalpha and beta were predominantly present in the cytosolic fraction, while membrane-associated PKCdelta was more prominent than that of cytosolic fraction; 2) the protein content of membrane-associated PKCalpha was significantly decreased at early (P < 0.05) and late (P < 0.01) sepsis; 3) there was no significant difference of protein contents of PKC-delta, -epsilon and -zeta between sham-operated and septic rat liver; 4) the activity of membrane-associated PKCalpha was significantly declined under detection level during sepsis; 5) at both early and late sepsis, the immunohistochemical staining of PKCalpha was significantly diminished, especially in the nucleus; 6) the RT-PCR product of PKCalpha mRNA of septic liver was significantly less than the sham-operated liver. These results suggest that inactivation and the suppression of PKC-alpha gene transcription might be involved in modulating hepatic failure during sepsis.

Localization, anchoring, and functions of protein kinase C isozymes in the heart

Although protein kinase C (PKC) was identified more than 20 years ago, and is involved in a wide variety of essential cellular processes, assigning specific roles to each PKC isozyme has proved difficult. Results over the last few years have suggested that much of the specificity of activated PKC isozymes is attributed to their subcellular localization bringing them into close proximity to a subset of substrates. Our laboratory has taken advantage of the importance of PKC localization and studied the way in which PKC isozymes are anchored. We have identified PKC anchoring proteins (RACKs or Receptors for Activated C Kinase) and used information about interaction sites between PKC isozymes and their respective RACKs to design peptides which modulate translocation of specific PKC isozymes to the functional site. These isozyme-specific peptides can be delivered into isolated or cultured cells or expressed in transgenic mice to determine the role of specific PKC isozymes in particular functions. Here we will describe the isozymes-specific peptide activators and inhibitors that we have developed and the specific functions of each isozyme in cardiac ventricular tissue.

Increased contractility and altered Ca(2+) transients of mouse heart myocytes conditionally expressing PKCbeta

Activation of protein kinase C (PKC) in heart muscle signals hypertrophy and may also directly affect contractile function. We tested this idea using a transgenic (TG) mouse model in which conditionally expressed PKCbeta was turned on at 10 wk of age and remained on for either 6 or 10 mo. Compared with controls, TG cardiac myocytes demonstrated an increase in the peak amplitude of the Ca(2+) transient, an increase in the extent and rate of shortening, and an increase in the rate of relengthening at both 6 and 10 mo of age. Phospholamban phosphorylation and Ca(2+)-uptake rates of sarcoplasmic reticulum vesicles were the same in TG and control heart preparations. At 10 mo, TG skinned fiber bundles demonstrated the same sensitivity to Ca(2+) as controls, but maximum tension was depressed and there was increased myofilament protein phosphorylation. Our results differ from studies in which PKCbeta was constitutively overexpressed in the heart and in studies that reported a depression of myocyte contraction with no change in the Ca(2+) transient.

Protein kinase C mediates neurite guidance at an astrocyte boundary

During development, astrocytes play an active role in directing axons to their final targets. This guidance has been attributed in part to the increased expression of guidance molecules, such as tenascin-C and chondroitin sulfate proteoglycans, by boundary-forming astrocytes. We have previously used a culture model of astrocyte boundaries to demonstrate that neurites growing on permissive astrocytes alter their trajectory as they encounter less-permissive astrocytes. The present study investigated the role of the protein kinase C (PKC) family of signal transduction molecules in this form of axonal guidance. Neurons were plated onto mixed astrocyte monolayers in the presence of agents that either downregulate the phorbol ester-sensitive PKC isoforms or inhibit PKC. Both downregulation and inhibition of PKC increased the percentage of neurons that crossed onto the nonpermissive astrocytes. On astrocyte monolayers, phorbol ester modulation of PKC but not PKC inhibitors resulted in a decrease in overall neurite extension. PKC inhibitors also caused a similar alteration in the neuronal response to cell-free boundaries, at concentrations that did not inhibit neurite extension. Thus, phorbol-ester-sensitive PKC isoforms direct the guidance of neurites by astrocyte-derived matrix molecules.

An antisense of protein kinase C-zeta inhibits proliferation of human airway smooth muscle cells

We hypothesized that an atypical isoform of protein kinase (PK) C, PKC-zeta, is essential for proliferation of human airway smooth muscle (HASM) cells in primary culture. Recombinant replication-deficient E1-deleted adenoviruses (100 plaque-forming units [pfu]/cell) expressing the antisense of PKC-zeta and the wild-type PKC-zeta (Ad-CMV-PKC-zeta) were added to actively growing cells that were subsequently incubated for 48 h in platelet-derived growth factor (PDGF) 40 ng/mL or 10% fetal bovine serum (FBS). Expression of the antisense at a virus concentration of 100 pfu/cell produced a significant (n = 3, P<0.05) decrease in the mean manual cell count in the presence of PDGF to 37+/-5% relative to that in cells with no virus (100%), whereas in cells infected with virus containing no construct, this figure was 102+/-13%. The increase in cell number in response to FBS, however, was not affected by the presence of the antisense. Corresponding values for cells in 10% FBS were 100+/-22%, 85+/-22%, and 122+/-18%. Western blotting revealed decreased levels of PKC-zeta protein, but not PKC-alpha or PKC-epsilon protein, in cells infected with the antisense when compared with levels in control cells. Thus, in HASM cells, PKC-zeta is involved in proliferation in response to PDGF, but not in response to FBS, for which alternate signal transduction pathways independent of PKC-zeta must exist.

Changes in protein kinase C isoforms in association with vascular hyporeactivity in cirrhotic rat aortas

BACKGROUND & AIMS

Although protein kinase C (PKC) alterations may play a role in the abnormal reactivity of cirrhotic rat aortas, its isoforms and cellular distribution are unknown. We therefore studied the protein expression and cellular distribution of PKC isoforms and their activation in cirrhotic rat aortas.

METHODS

Endothelium-denuded aortas from control and cirrhotic rats were examined. Immunoblots were performed with PKC isoform-specific antibodies. Aortic reactivity was determined for phorbol myristate acetate and phenylephrine after PKC down-regulation.

RESULTS

PKC-alpha expression was reduced in both the cytosolic and membrane fractions in cirrhotic aortas. Trace amounts of PKC-beta were detected in cirrhotic aortas. PKC-delta was detected in the cytosolic fraction of control and cirrhotic aortas. PKC-zeta was detected in the membrane fraction in control aortas and in the cytosolic fraction in cirrhotic aortas. Phorbol myristate acetate and phenylephrine triggered translocation of PKC-alpha and PKC-delta isoforms from the cytosol to the membrane in control aortas; in cirrhotic aortas, only PKC-alpha was translocated. Aortic reactivities were reduced after PKC down-regulation. PKC-alpha and -delta activities were reduced in cirrhotic aortas.

CONCLUSIONS

These results suggest that a change in PKC isoforms may be responsible in part for the abnormal reactivity and intracellular transduction through the PKC pathway in cirrhotic rat aortas.

Angiotensin II-induced decrease in expression of inducible nitric oxide synthase in rat astroglial cultures: role of protein kinase C

Inducible nitric oxide synthase (iNOS) has been implicated as a mediator of cellular toxicity in a variety of neurodegenerative disorders. Nitric oxide, which is generated in high quantities following induction of iNOS, combines with other oxygen radicals to form highly reactive, death-inducing compounds. Given the frequency of neuronal death due to neurodegenerative diseases, cerebral trauma, and stroke, it is important to study the mechanisms of regulation of iNOS in the brain. We demonstrated previously that angiotensin II (Ang II) decreases the expression of iNOS produced by bacterial endotoxin or cytokines in cultured astroglia prepared from adult rat brain. Here, we have addressed the mechanisms by which Ang II negatively modulates iNOS. The inhibitory effects of Ang II on lipopolysaccharide-induced expression of iNOS mRNA and protein and nitrite accumulation were mimicked by the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate. Down-regulation of PKC produced by long-term treatment of astroglia with phorbol 12-myristate 13-acetate abolished the inhibitory effect of Ang II on lipopolysaccharide-stimulated expression of iNOS mRNA and nitrite accumulation. Finally, the reduction of lipopolysaccharide-induced nitrite accumulation by Ang II was attenuated by the selective PKC inhibitor chelerythrine. Collectively, these data indicate a role for PKC in the inhibitory actions of Ang II on iNOS expression in cultured astroglia.

Structure and genomic organization of porcine RACK1 gene

The cDNA encoding porcine RACK1 protein was isolated from porcine spleen cDNA library. The deduced protein sequence of porcine RACK1 cDNA shows that it contains 317 amino acid residues, and shares nearly 100% identity with its vertebrate counterparts. Noticeably, the RACK1 protein was differentially expressed in various porcine tissues. High expression of RACK1 protein was observed in the tissues including thymus, pituitary, spleen and liver, whereas there was no detectable expression in muscle. The genomic DNA of porcine RACK1 with approximate 7.5 kb was constructed by both polymerase chain reaction amplification and genomic library screening. It consists of eight exons intervened by seven introns, and most of the intron/exon splice sites conform to the GT/AG rule. The promoter region contains functional serum response element, YY1-like binding site and AP1 site, which is supported by the finding that the expression of RACK1 gene in cultured porcine ST cells has a serum response as well as a TPA response.

Protein kinase C expression and subcellular distribution in chronic myocardial ischemia. Comparison of two different canine models

We studied protein kinase C (PKC) isozyme expression and activity distribution in two models of chronically ischemic canine myocardium: (1) single vessel obstruction (SVO), produced by tight stenosis of LAD followed by preconditioning and acute ischemia (40 min); (2) three vessel obstruction (3VO), produced by LAD-stenosis and gradual occlusion of right coronary artery and left circumflex. In both models after 8 weeks of chronic ischemia the dogs were either sacrificed or had PTCA of the LAD with a follow up of another 4 weeks. Control dogs were sham operated. PKC activity was measured in subcellular fractions of tissue samples from anterior and posterior regions in the presence of histone and gamma-[32P]-ATP. PKC isozymes were detected by Western blotting. All regions perfused by the obstructed coronaries were dysfunctional at 8 weeks when compared to baseline, with improvement of anterior wall function after PTCA of LAD. PKC activity was elevated in the membrane fraction of SVO, but unchanged in the 3VO model. PKCs alpha, epsilon, and zeta prevailed in cytosol fraction of the controls (cytosol/membrane ratios were +/- 3.34, 1.38 and 4.56 for alpha, epsilon and zeta, respectively), consistent with PKC activity distribution, while delta was not detected. There was no significant difference between the groups concerning the relative membrane amount of the isozymes. PKCs alpha and epsilon were decreased in the cytosol fraction of both models at 8 weeks (for anterior region, by 56 and 57% in SVO and by 49 and 46% in 3VO, respectively) without there being any differences between anterior and posterior regions, and were low also in the PTCA group. PKC zeta distribution however varied between the two models. The amount of PKC zeta isozyme was downregulated by 45% after 8 weeks of chronic ischemia and returned towards the control values after PTCA in the anterior region of SVO, while it did not change in anterior wall after 8 weeks in 3VO but was significantly decreased (by 47%) in posterior region after PTCA. In conclusion, our results suggest modified PKC signalling in chronically ischemic canine myocardium.

Protein kinase C isoforms in human airway smooth muscle cells: activation of PKC-zeta during proliferation

Protein kinase C (PKC) is implicated in the regulation of smooth muscle contractility and growth. We have previously described the pattern of isoform expression of PKC in canine airway smooth muscle. This study identified the isoforms present in human cultured airway smooth muscle cells and also addressed the question of whether mitogenesis in these cells is associated with changes in a specific isoform, PKC-zeta. Western blot analysis revealed the presence of PKC-alpha, -betaI, and -betaII of the conventional group; PKC-delta, -theta, -epsilon, and -eta of the novel group; and PKC-zeta, -mu, and -iota of the atypical group. There was a significant increase in density of the Western blot for PKC-zeta in cells proliferating in response to 10% fetal bovine serum (FBS) to 372 +/- 115% of control values (P < 0.05; n = 3 patients) in the cytosolic fraction. Platelet-derived growth factor (PDGF) produced increases in PKC-zeta in both the cytosolic and membrane fractions to 210 +/- 49 and 443 +/- 227%, respectively, of control values (P < 0.05; n = 4 patients). There was no change in expression of PKC-alpha, -betaI, -betaII, -theta, -epsilon, -eta, -delta, or -iota in response to the same stimuli. PGE2 (1 microM) added to the cells 30 min before PDGF reduced incorporation of [3H]thymidine from 5,580 +/- 633 (SE) to 3, 980 +/- 126 dpm (P < 0.05; n = 3 patients) and, in addition, reduced expression of PKC-zeta in the membrane fraction as determined by Western blotting from 266 +/- 66 to 110 +/- 4% of control values (P < 0.05; n = 3 patients). PKC-zeta activity in stimulated cells (10% FBS), as assessed by immunoprecipitation and phosphorylation of glycogen synthase peptide, was approximately 3-fold greater than that in unstimulated cells, and the amount of PKC-zeta protein correlated with isoenzyme activity (r2 = 0.91; P < 0.02; n = 4 patients). In conclusion, this study 1) provides the first description of which isoforms of PKC are present in human cultured airway smooth muscle cells and 2) shows that proliferation of these cells is associated with upregulation of PKC-zeta. Whether activation of PKC-zeta is a primary or secondary event in airway smooth muscle cell proliferation remains to be determined.

Increased protein kinase C activity and expression of Ca2+-sensitive isoforms in the failing human heart

BACKGROUND

Increased expression of Ca2+-sensitive protein kinase C (PKC) isoforms may be important markers of heart failure. Our aim was to determine the relative expression of PKC-beta1, -beta2, and -alpha in failed and nonfailed myocardium.

METHODS AND RESULTS

Explanted hearts of patients in whom dilated cardiomyopathy or ischemic cardiomyopathy was diagnosed were examined for PKC isoform content by Western blot, immunohistochemistry, enzymatic activity, and in situ hybridization and compared with nonfailed left ventricle. Quantitative immunoblotting revealed significant increases of >40% in PKC-beta1 (P<0.05) and -beta2 (P<0.04) membrane expression in failed hearts compared with nonfailed; PKC-alpha expression was significantly elevated by 70% in membrane fractions (P<0.03). PKC-epsilon expression was not significantly changed. In failed left ventricle, PKC-beta1 and -beta2 immunostaining was intense throughout myocytes, compared with slight, scattered staining in nonfailed myocytes. PKC-alpha immunostaining was also more evident in cardiomyocytes from failed hearts with staining primarily localized to intercalated disks. In situ hybridization revealed increased PKC-beta1 and -beta2 mRNA expression in cardiomyocytes of failed heart tissue. PKC activity was significantly increased in membrane fractions from failed hearts compared with nonfailed (1021+/-189 versus 261+/-89 pmol. mg-1. min-1, P<0.01). LY333531, a selective PKC-beta inhibitor, significantly decreased PKC activity in membrane fractions from failed hearts by 209 pmol. min-1. mg-1 (versus 42.5 pmol. min-1. mg-1 in nonfailed, P<0.04), indicating a greater contribution of PKC-beta to total PKC activity in failed hearts.

CONCLUSIONS

In failed human heart, PKC-beta1 and -beta2 expression and contribution to total PKC activity are significantly increased. This may signal a role for Ca2+-sensitive PKC isoforms in cardiac mechanisms involved in heart failure.

Pituitary expression of protein kinase C isotypes during early development

Protein kinase C (PKC) is a critical regulator of signal transduction and cell function in many tissues, including pituitary. Although PKC influences pituitary hormone secretion in adults, its role in determining characteristic perinatal patterns of hormone secretion and synthesis is not known, and the expression of major PKC isotypes in perinatal pituitary is poorly defined. We therefore determined the developmental, cell-specific expression of the major PKC isotypes, using Western analysis and double label immunohistochemistry, in pituitaries of perinatal and mature rats. Expression of specific PKC isotypes was strikingly age-dependent. Pituitary expression of PKC alpha was particularly high in neonates and declined significantly with age, with levels in adult rats approximately half those of neonates as assessed by Western analysis. Similarly, immunohistochemistry indicated that PKC alpha was less abundant in adult than in neonatal pituitaries; the most intensely staining cells of both age groups were identified as somatotrophs and gonadotrophs. In contrast to PKC alpha, pituitary expression of PKC epsilon increased approximately two-fold with advancing age as assessed by Western analysis; this age-dependent pattern was confirmed by immunohistochemistry. Perinatal pituitaries expressed PKC epsilon in some somatotrophs and in all gonadotrophs, whereas PKC epsilon expression was limited to gonadotrophs in the mature pituitary. Pituitary expression of PKC betaII, delta, and zeta did not differ with age, and PKC gamma was not detected in pituitaries of any age group. These results indicate that expression of PKC isotypes within the pituitary is developmentally regulated in a cell-specific and isotype-specific manner, and are consistent with the concept that PKC contributes to the regulation of pituitary function during early development.